docs: def append(self, item):
          """Append `item` (:class:`StyledText` or :class:`str`) to the end of
          this mixed-styled text.
  
          The parent of `item` is set to this mixed-styled text."""
          if isinstance(item, str):
              item = SingleStyledText(item)
          item.parent = self
          list.append(self, item)